The present invention relates to a new and distinct cultivar of Hydrangea macrophylla and will be referred to hereafter by its cultivar name, ‘Horthamp’. ‘Horthamp’ represents a new bigleaf hydrangea, a perennial shrub grown for landscape use.
‘Horthamp’ was derived from an ongoing controlled breeding program directed by the Inventor in Boskoop, The Netherlands. The objective of the breeding program was to develop new cultivars of Hydrangea with sterile flower sepals that are picotee with pink or red edges. ‘Horthamp’ arose from a controlled cross made by the Inventor in June of 2008 between unnamed and unpatented proprietary plants in the Inventor's breeding program; reference no. 07-036-01 as the female parent and reference no. 07-120-04 as the male parent. ‘Horthamp’ was initially selected a single unique plant from amongst the resulting seedlings for further evaluation in 2010 and characteristics confirmed in June of 2013.
Asexual propagation of the new cultivar was first accomplished by stem cuttings by the Inventor in Boskoop, The Netherlands in July of 2010. Asexual propagation by stem cuttings has determined that the characteristics of the new cultivar are stable and are reproduced true to type in successive generations.